A common manner of manufacturing a large voltage source capable of outputting a relatively large voltage is to connect in series a plurality of smaller voltage sources, each of which is capable of generating a relatively small voltage. The relatively small voltages generated by the plurality of smaller voltage sources connected in series cumulatively result in generation of the relatively large voltage. Such a technique is common and is used, for example, when generating a relatively large voltage using a stack of fuel cells or a series connection of battery cells for use in an electric vehicle.
Some challenges that arise when generating a relatively large voltage using a series connection of smaller voltage sources include those of inexpensively, accurately, quickly and simultaneously obtaining voltage measurements of any one of the smaller voltage sources. For example, when generating a relatively large voltage using a stack of fuel cells, monitoring the voltage generated by the individual fuel cells in the stack is important, for example, to ensure that the power being drawn from the stack does not force any individual cell into a detrimental or undesirable operating range. When generating a relatively large voltage using a series connection of battery cells in an electric vehicle, monitoring the voltage of individual battery cells is important, for example, to ensure that no cell is operating in an overcharged or undercharged state, as operation in such states can decrease overall battery performance and reduce battery life.
While systems and methods exist for measuring the voltage of individual or small groups of such smaller voltage sources, such systems and methods are lacking in several respects. Conventional systems and methods typically are limited to common mode voltage abilities of approximately 200 to 300 Volts, and their ability to be used in conjunction with a large voltage source capable of generating, for example, 1 kV or more is limited. Furthermore, conventional systems and methods are not very accurate, often having accuracies limited to about +/−5 mV.
Accordingly, there exists a need for a system and method for monitoring voltages that improves on at least one of the deficiencies of the prior art.